1. Field of the Invention
This invention relates to an apparatus for punching precision holes and in particular a device for punching precision holes in material used for mounting multiple integrated circuits and for creating holes used for interchip connections in the precision punched material.
2. Description of Related Art
Circuit boards with multiple VLSI circuit chips are called Multichip Modules (MCM). The use of VLSI circuits present interface problems relating to the interconnection of the integrated circuits to other circuits and the placement of the integrated circuits on a ceramic circuit board (MCM-C). As VLSI technology has advanced, the density of circuits on a single VLSI chip has increased and the necessary interconnection for VLSI chips has become increasingly difficult to achieve in a limited space. An MCM-C design object is to increase the ratio of the total area occupied by silicon to the total board area, called silicon efficiency ratio. The MCM-C packaging limits the speed and size of a system. Since the physical interconnection is a the limiting design factor, a means of accommodating more circuit interconnections is necessary.
In a typical configuration, semiconductor chips are mounted in cavities on multilayer circuit boards, the circuit boards accommodate intercircuit connections through tiny vertical holes or VIAs between the layers. The chips are connected to the VIAs using a controlled-collapsed-chip-connection technique called C-4. The VIAs are filled with a conductive material, such as molybdenum paste, which creates a connection to the VLSI circuit. The size of the holes dictates the size of the connection and the number of connections that can be facilitated on the multilayer circuit board.
There are a number of methods for creating small holes in precision tooling for facilitating the punching of VIAs including laser cutting and electrical discharge machining. The precision tooling of each of these methods facilitates the punching of VIA holes as small as 0.01778 cm (0.007 in.) in dielectric material as thin as 0.00762 cm (0.003 in.). The precision tooling is used in a master punch and die assembly.
In the precision punching method, each precision VIA hole is punched in a workpiece or substrate using precision tooling which includes a precision punch assembly and a precision die assembly. The punches of the precision tooling device are guided by precision holes in one or more precision plates. The cutting edge of the die plate is formed by precision openings in the die plate. The precision of the tooling is the limiting factor in providing a precision punched substrate. Prior art is directed to the precision necessary for the creation of the smallest possible precision holes in a substrate.
The VIAs necessary to create the circuit interconnection have previously been created by a punch and die device which is fabricated by making a die mask or plate using electrical discharge machining (EDM). The plate is fabricated from 0.127 cm (0.050 in.) tool steel. Precision holes as small as 0.01651 cm (0.0065 in.) are burned through two plates at one time by EDM at a rate of approximately 6 holes per hour. The plates are then used in a precision tooling device. The size of the substrate hole punched by the precision tooling is limited by the size of the smallest plate opening which can be created by EDM, 0.01651 cm (0.0065 in.). The EDM plate facilitates punching holes with an accuracy of 0.00762 cm (0.003 in.) true position. These tool steel plates are heavy, expensive and require sharpening. The sharpening is time consuming and can only be done several times before the die must be replaced due to wear.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a punch and die for punching precision holes whereby true position accuracy is improved.
It is another object of the present invention to provide a die which is much lighter in weight than prior art dies.
A further object of the present invention is to provide a device which has lower cost to construct.
A further object of the present invention is to provide a device which punches the smallest possible precision holes in a substrate.
A further object of the present invention is to provide a device which punches straighter holes than prior art devices.
It is yet another object of the present invention to provide a device to punch precision holes in variable patterns.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.